The present invention is directed to ink compositions and imaging and printing processes thereof. More specifically, in one embodiment the present invention is directed to rapid drying fluorescent ink jet ink compositions useful in the printing of concealed images for security or encoding applications, and wherein the inks contain dyes based on a porphyrin chromophore, or analogous components and a dendrimer, or mixture of dendrimers. The dyes can possess an extremely strong band at 380 to 500 nanometers, the Soret Band of the absorption spectrum, in addition to much weaker bands in the 600 to 800 nanometer range. The dyes also exhibit fluorescence in the 600 to 800 nanometer range, which spectral area is distinct from the emission window characteristic of the optical brighteners used in commercial papers. In one embodiment, the inks of the present invention are comprised of the porphyrin chromophore dye, like tetrapyridiniumporphyrin tetraacetate, an aqueous liquid vehicle optionally containing solvents, and a dendrimer. The inks can be formulated after mixing water, the dendrimer, and the dye by the addition, for example, of a cosolvent comprised of water and a glycol, like diethyleneglycol, thereby improving latency, which is the maximum time period, for example less than one hour, and from about 1 to about 10 minutes, over which an uncapped ink jet printhead can remain idle before noticeable deterioration of its jetting performances, and this addition can improve ink drying time, that is the time needed for an ink jet print to dry to an extent such that it will not smear or offset upon handling or when placed in contact with another sheet of paper, which drying time can, for example, be less than one minute, or more specifically from about 0.2 to about 5 seconds. Also, the addition of glycol permits the adjustment of the ink viscosity from about 1.1 to about 5 centipoise, and preferably from about 1.1 to about 3.0 centipoise, and can permit adjustment of the ink surface tension. Viscosity and surface tensions are major contributing factors in the production of excellent quality prints on plain papers, that is prints with acceptable edge acuity, or the sharpness of the edge between the printed and nonprinted areas, minimal ink feathering on paper, and characterized, for example, by a desirable uniformity of solid area ink coverage. The inks of the present invention can be selected for a number of known ink jet printing methods and apparatus, including thermal ink jet, or bubble jet processes as described in, for example, U.S. Pat. Nos. 4,601,777, 4,251,824, 4,410,899, 4,412,224, and 4,532,530, the disclosures of which are totally incorporated herein by reference. More specifically, the inks of the present invention can be selected to generate invisible images which can be made visible to certain users under special viewing conditions, such as illumination of the image with ultraviolet light. These images can be detected also by sensors, such as detectors of fluorescence.
The fluorescent inks of the present invention are especially useful for the printing of concealed images for security applications, such as printing of documents containing information restricted to a limited readership. The inks of the present invention are also especially useful in processes wherein it is desired to place invisible markings on documents; examples of such situations include providing security markings to control the number of copies made of a document, providing invisible markings that can be detected by an imaging device and that provide instructions to the imaging device, identifying the machine with which the original document was made, or controlling the integrity of a printing job, or monitoring downstream functional operations, or the like. These inks contain in addition to dendrimers a fluorescent dye selected from a number of dyes which are compatible with specific solvent mixtures known to provide inks which dry rapidly, for example from between 0.2 to 5 seconds, when, for example, jetted on office papers. Rapid drying and excellent waterfastness, in embodiments from between 90 to about 99 percent, are of value in rapid printing applications such as printing by xerography at a speed of 50 to 100 copies per minutes, like those related to document tagging. Also, in embodiments the inks of the present invention possess water staining resistance.
Ink jet printing systems can generally be classified by two known types, continuous stream and drop-on-demand. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not usually formed or expelled unless it is to be placed on the recording medium. A second type of drop-on-demand system is known as thermal ink jet, or bubble jet. With this type, there are apparently generated high velocity droplets and there is allowed very close spacing of the nozzles. Thermal ink jet processes are well known as indicated herein, and are described, for example, in U.S. Pat. Nos. 4,601,777; 4,251,824; 4,410,899; 4,412,224 and 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Known ink jet inks generally comprise a water soluble dye which is soluble in an ink vehicle such as water or a mixture comprising water and a water soluble or water miscible organic solvent. Inks comprising soluble dyes may exhibit many problems, such as poor waterfastness, poor lightfastness, clogging of the jetting channels as a result of solvent evaporation and changes in the solubility of the dye, dye crystallization, ink bleeding when prints are formed on plain papers, poor thermal stability, chemical instability, ease of oxidation, and low drop velocity. In addition, many of the dyes contained in inks may be potentially toxic or mutagenic. These problems can be minimized by replacing the dyes used in ink formulations with insoluble pigments. In general, pigments are superior to dyes with respect to waterfastness, lightfastness, image density, thermal stability, oxidative stability, the ability to perform intercolor ink mixing, compatibility with both coated/treated and plain papers, image edge acuity, reduced image feathering, and nontoxic and nonmutagenic properties.
Heterophase ink jet inks are known. For example, U.S. Pat. No. 4,705,567, the disclosure of which is totally incorporated herein by reference, discloses a heterophase ink jet ink composition which comprises water and a dye covalently attached to a component selected from the group consisting of poly(ethylene glycols) and poly(ethylene imines), which component is complexed with a heteropolyanion. In addition, U.S. Pat. No. 4,597,794 discloses an ink jet recording process which comprises forming droplets of an ink and recording on an image receiving material by using the droplets, wherein the ink is prepared by dispersing fine particles of a pigment into an aqueous dispersion medium containing a polymer having both a hydrophilic and a hydrophobic construction portion. The hydrophilic portion constitutes a polymer of monomers having mainly polymerizable vinyl groups into which hydrophilic portions such as carboxylic acid groups, sulfonic acid groups, sulfate groups, and the like are introduced. Pigment particle size may be from several microns to several hundred microns. The ink compositions disclosed may also include additives such as surfactants, salts, resins, and dyes.
U.S. Pat. No. 4,877,451, the disclosure of which is totally incorporated herein by reference, discloses ink jet ink compositions comprising water, a solvent, and a plurality of colored particles comprising hydrophilic porous silica particles to the surfaces of which dyes are covalently bonded through silane coupling agents. In addition, copending application U.S. Ser. No. 07/369,003, the disclosure of which is totally incorporated herein by reference, there are illustrated ink jet inks and liquid developers containing colored particles comprising hydrophilic porous silica particles to the surfaces of which dyes are covalently bonded through silane coupling agents. The ink compositions of this patent are believed to be less stable in the printheads, and less stable during storage, disadvantages avoided, or minimized with the inks of the present invention.
Copending application U.S. Ser. No. 544,564 (now abandoned), the disclosure of which is totally incorporated herein by reference, relates, for example, to ink compositions which comprise an aqueous liquid vehicle and colored particles of an average diameter of 100 nanometers or less which comprise micelles of block copolymers of the formula ABA, wherein A represents a hydrophilic segment and B represents a hydrophobic segment, and wherein dye molecules are covalently attached to the micelles. In a specific embodiment of the copending application, the colored particles comprise micelles of block copolymers of the formula ABA having silica precipitated therein and dye molecules covalently attached to the micelles.
In U.S. Pat. No. 5,120,361, the disclosure of which is totally incorporated herein by reference, there is disclosed an ink composition comprised of a solution comprised of a dendrimer and a dye or dyes, which dyes are visible, or can be seen under normal viewing conditions, and wherein the dendrimer can be a first, second or third generation dendrimer.
U.S. Pat. No. 5,225,900, entitled "Method of Storing Information Within a Reprographic System", with the named inventor Joseph D. Wright, the disclosure of which is totally incorporated herein by reference, discloses apparatuses and processes for controlling a reproduction system by scanning an image to detect at least one taggant in at least one marking material forming the image and issuing instructions to the reproduction system; the instructions cause the reproduction system to take an action selected from the group consisting of (a) prohibiting reproduction of those portions of the image formed by a marking material containing at least one predetermined detected taggant and reproducing all other portions of the image; (b) prohibiting reproduction of any part of the image upon detection of at least one predetermined taggant; (c) reproducing only those portions of the image formed by a marking material containing at least one predetermined taggant; (d) reproducing portions of the image formed by a marking material containing at least one predetermined taggant in a different manner from that in which the system reproduces portions of the image formed by a marking material not containing at least one predetermined taggant; and (e) identifying a source of the image on the basis of detection of at least one predetermined taggant.
In U.S. Pat. No. 5,145,518 there is disclosed an ink composition which comprises an aqueous liquid vehicle and particles of an average diameter of 100 nanometers or less which comprise micelles of block copolymers of the formula ABA, wherein A represents a hydrophilic segment and B represents a hydrophobic segment, and wherein dye molecules are covalently attached to the micelles, said dye molecules being detectable when exposed to radiation outside the visible wavelength range; and in copending application U.S. Ser. No. 834,093 there is disclosed an ink composition comprised of a solution comprised of a dye comprised of a porphyrin chromophore. The disclosures of each of these patents and copending applications are totally incorporated herein by reference.